In the media printing environment it is important to assure that a printing onto a media is performed accurately. For example, in an inkjet printer environment, if the inkjet printhead is out of alignment, the ink will not print on a media in the proper position. To verify the alignment of a printing apparatus, typically an alignment detector is utilized to review predetermined marks made on a media to determine whether the printing apparatus that printed such marks is in alignment.
The alignment detector typically includes at least three components, a light source, an alignment sensor, and a housing to hold both the light source and the sensor, though the housing is not necessary.
Many ink jet printers include a printhead auto-alignment detector that may be used to automatically calculate and correct for various printhead misalignments including, for example, horizontal misalignment between two printheads, vertical misalignment between two printheads, bi-directional misalignment of a printhead, and skew misalignment of a printhead. The auto-alignment detector typically includes at least three components, a light source, an alignment sensor, and a housing to one printer configuration, for example, the printer performs printhead auto-alignment using a carrier mounted printhead auto-alignment detector that moves with the printhead carrier across a printed test pattern of ink marks or blocks.
For example, one known technique to determine bi-directional misalignment is to print a plurality of rectangular blocks along the main scanning axis, i.e., the scanning axis of the printhead, with odd blocks printed from left to right and with even blocks printed from right to left with the intent of placing an even block exactly midway between two adjacent odd blocks. After printing, in one technique, the sensor is passed over the pattern to measure the distances between adjacent blocks, such as for example, by using the position encoder of the printhead carrier or by using a timer and the known speed of the sensor. Unequal distances are a measure of bi-directional misalignment which, in one technique, is corrected for by advancing or delaying the firing times when printing right to left so that, in the case of the test pattern, the blocks from bi-directional printing are printed an equal distance apart.
Ink jet printers and all-in-one (AIO) devices that include a scanner part and a printer part have increased their reliance on auto alignment, and there is a desire to place more and more information on the auto alignment page. Examples of auto alignment technology for ink jet printers and all-in-one (AIO) devices that include a scanner part and a printer part are described in U.S. Pat. Nos. 7,044,573; 6,655,777; 6,616,261; 6,485,124; 6,450,607; and 6,281,908, all of which are incorporated herein by reference.
Many current Ink jet printers and all-in-one (AIO) devices that include a scanner part and a printer part have an auto-alignment feature that uses two LED's and a sensor to align each color ink individually. The LED's are different colors because each ink has a different peak reflectance wavelength and one color of LED may “see” one ink well, but not another. For example, when the auto-alignment detector only used a red LED, the cyan nozzles could be aligned well and the magenta nozzles could be aligned with a little more optimization but the yellow nozzles could not be aligned. With a red LED, the yellow ink was not distinguishable from the white paper. A blue LED has to be added to the auto-alignment detector so that the yellow nozzles could be aligned.
What is needed in the art is a method for simplifying the auto-alignment detection by only requiring the use of a single LED and further, to improve the performance for auto-alignment and any color correction method integrated into the printer.